In recent years, droughts have increasingly disrupted the delicate balance within Europe’s forest ecosystems, with climate change amplifying the frequency and severity of these events. A groundbreaking study spearheaded by the German Center for Integrative Biodiversity Research (iDiv) alongside Leipzig University sheds light on an astonishing mechanism by which forests maintain resilience during drought conditions. Contrary to the traditional focus on species richness alone, this research reveals that the key to drought resistance lies in the diversity of the trees’ hydro-functional traits—how individual species absorb, store, and utilize water. These functional differences serve as a vital buffer, stabilizing forests under environmental stress.
The research builds on the MyDiv tree diversity experimental plots in Bad Lauchstädt, Saxony-Anhalt, where over 2,600 trees across ten native European species were meticulously monitored over a six-year span, including the extraordinary drought period from 2018 to 2020. The intensive dataset allowed researchers to examine growth metrics in the context of 14 distinct hydro-functional traits, ranging from water transport efficiency to stomatal regulation. This approach goes beyond classical biodiversity indexes by focusing on the physiological mechanisms underlying drought response, opening novel pathways for forest ecology and management.
One of the most compelling insights from the study is the recognition of contrasting drought survival strategies among tree species. Species such as oak demonstrate remarkable hydraulic safety, meaning their vascular tissues effectively maintain water flow under drought stress, which preserves growth capacity. Conversely, species like birch exhibit vulnerability to extended drought durations, showing reduced growth during dry years. Yet, these same resilient species may falter when water is abundant, highlighting a profound ecological trade-off between drought resistance and optimal growth in mesic conditions. This dynamic underscores the complexity of forest ecosystems, where no single strategy guarantees superiority year-round.
Central to the study’s findings is the concept that a forest stand’s collective performance during drought is not merely a function of how many species coexist but how differently these species manage water. Trees surrounded by neighbours employing dissimilar hydro-functional strategies enjoyed enhanced growth resilience during droughts, suggesting that functional trait diversity acts as a biological insurance policy against environmental extremes. This discovery revolutionizes the way forest management and conservation think about species mixtures, emphasizing functionality over taxonomic diversity for ecosystem stability.
Further mechanistic understanding stems from detailed assessments of stomatal behavior—a key physiological control point regulating transpiration and gas exchange. Trees capable of precise stomatal closure can minimize water loss during drought without completely halting photosynthesis, thus sustaining growth. Meanwhile, trees less adept at controlling stomata under stress experience hydraulic failure and growth decline. Hydro-functional trait dissimilarity within neighborhoods allows complementary water use patterns, reducing direct competition for water and ensuring more efficient collective resource use under stress.
The implications for forest management are profound. Mixed-species forests assembled to maximize diversity in hydro-functional traits could inherently buffer against increasing drought frequencies projected under climate change scenarios. By strategically selecting species based not only on taxonomy but on physiological functions related to water usage, foresters can enhance forest stand stability and maintain ecosystem services. Such functional diversity could offset the detrimental impact of drought-induced diebacks, safeguarding biodiversity, carbon storage, and timber productivity.
Beyond immediate drought resilience, the study also highlights the need for a deeper exploration of hydro-functional traits in a broader range of species, including those anticipated to migrate northward as climates warm. iDiv’s ongoing ARBOfun program, which examines water relations in nearly 100 tree species, aims to build a comprehensive hydro-functional trait database. This database will be instrumental in guiding species selection for future forest compositions tailored to anticipated climatic realities, potentially transforming forest restoration and afforestation strategies on a continental scale.
While the study harnessed detailed trait measurements to unlock these insights, it also emphasizes the ecological principle that ecosystem function emerges from the interplay of individual species’ traits rather than species presence alone. This focus on trait-based ecology represents an innovative shift that could inform predictive modeling of forest responses to climate stressors, fostering more adaptive management paradigms. The recognition that functional trait dissimilarity enhances drought resilience aligns with broader ecological theories, reinforcing the value of diverse physiological strategies within plant communities.
Importantly, the research highlights a temporal dimension to drought resilience strategies. Trees that thrived during intense drought years were often those at a disadvantage in wetter periods. Such context-dependent performance highlights the dynamic nature of ecological fitness and underscores the importance of forest heterogeneity in stabilizing productivity over variable climatic cycles. Recognizing these temporal trade-offs can assist scientists and managers in anticipating forest trajectories under fluctuating environmental conditions.
The MyDiv experiment, in continuous operation since 2015, provides a uniquely long-term and large-scale framework to analyze the interplay between species interactions, mycorrhizal associations, and ecosystem functions such as carbon cycling and water regulation. By integrating hydro-functional traits into this experimental design, the research team has provided invaluable empirical evidence for the benefits of functional diversity in real-world forest ecosystems, helping bridge the gap between theory and practice.
In summary, this pioneering research elucidates how the complex tapestry of water-use strategies among tree species underpins the resilience of European forests amid escalating drought stress. It challenges conventional biodiversity paradigms, suggesting that future-proofing forests against climate change requires embracing functional diversity at the physiological level. As droughts threaten global forest health, such insights offer hope for maintaining the vitality and services of forests in an uncertain climatic future.
Subject of Research: Forest drought resilience, hydro-functional traits, functional diversity, tree physiology, climate change adaptation
Article Title: Hydro-functional traits and their dissimilarity to the neighbourhood buffer tree growth against the 2018-2020 Central European drought
News Publication Date: 13-Nov-2025
Web References: DOI link
Image Credits: Lena Sachsenmaier
